EARTH SCIENCE 110: Introduction to Geology
Dr. Christopher Woltemade
Name: _____________________________
Section: ___________________________
Streams Field Exercise
Goals: Completing this exercise will give you first-hand experience with many stream features and
introduce you to the stream channel and wetland restoration project on Burd Run, Shippensburg, PA.
Materials: You should first read the Woltemade and Wood (2002) article, available on-line from the
course web page. You will need to refer to this article to answer some of the questions. A trail guide
brochure has also been provided. You should wear shoes that you don’t mind getting dirty or wet.
Instructions: Go to the Shippensburg Township Park, located along Burd Run on Britton Road (near
the access road to the SU Spiritual Center) and spend an hour or so walking along the creekside trail.
As you walk, answer the questions below and identifying the features listed in bold.
Trail beginning / Overview sign
Enter the trail along the stream near the parking lot, stopping to read the large sign:
1.
Flow in Burd Run contributes to what downstream watersheds (name three)?
________________________
2.
________________________
_______________________
Into what body of salt water does this water eventually flow?
_____________________________
Look at the limestone outcrop across Britton Road. These rocks are over 450 million years old.
Notice that the rock layers are dipping steeply into the ground (they have been tilted significantly since
original deposition in horizontal layers). Because limestone, a carbonate rock, dissolves in contact with
weak acids (precipitation and ground water), there are enlarged bedding planes and joints in the rock
that allow water to easily flow through it. This provides a pathway for pollutants to travel from
surrounding land uses into the groundwater. You will revisit this story at the end of your park visit.
3.
Based on earlier experiences in this course, what environment did this limestone form in?
Circle one: deep ocean stream valley beach
As you first come to the stream’s edge, look upstream under the Britton Road bridge. This stream
section is relatively steep, generating high flow velocities through the bridge, especially during floods.
Notice that this rapidly flowing water is directed toward the cut bank of a meander bend, which is
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protected by rip-rap, trees (from live stakes), and rock vanes. These features minimize bank erosion
and direct the water away from the stream bank, toward the center of the channel. On the far side of the
stream channel you should see a point bar on the inside of the bend.
4.
What size of sediments make up the surface of the point bar? Circle one: gravel
sand
silt
The point bar sediments are not derived from the local limestone (note the different color). They have
been transported a few miles from South Mountain and are only temporary stored here before being
transported further downstream in the next flood.
Interpretive sign #1.
Walk downstream to the first small sign along the stream, which indicates a vortex rock weir. It is
difficult to see the structure in the stream, as it is largely covered with water and sediment, but you can
see a photo of the complete structure during construction on the sign.
5. What is the purpose of this rock structure?
________________________________________________________________________
________________________________________________________________________
Interpretive sign #2.
Throughout the park, the stream channel constantly changes from pools to riffles. You can complete
the following questions anywhere along the stream where you see riffles and pools.
6. What size sediment dominates the streambed at riffles? Circle one: gravel sand silt
7. At a riffle, throw a leaf or small stick into the water and time it as it floats for a distance of 10 feet.
What is the velocity of the water?
(Distance = 10 feet / Time elapsed = _________ seconds) = _______ feet / second
8. What size sediment dominates the streambed at pools? Circle one: gravel sand silt
9. At a pool, throw a leaf or small stick into the water and time it as it floats for a distance of 10 feet.
What is the velocity of the water?
(Distance = 10 feet / Time elapsed = _________ seconds) = _______ feet / second
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Interpretive sign #3.
The root wads and log vanes here are difficult to see in the stream, as they are now several years old
and are largely overgrown. Examine the photos and the interpretation on the sign. If you look around
carefully, you should be able to see root wads in the stream bank on the outside of bends (there are a
total of 11 in the entire park).
10. What is the purpose of the root wads?
________________________________________________________________________
________________________________________________________________________
Interpretive sign #4.
Here you find a description of rip-rap, which has been placed near the bridge (large rocks to protect
against high-energy flow) and on other bends (smaller rocks were used where erosive power is not as
high as near the bridge). There is also information on live stakes.
11. What tree species are the live stakes?
_____________________________
12. Estimate the current height of the trees that have grown from the live stakes (note there are
hundreds of these trees right along the channel—they have lots of thin, wispy branches and small
leaves). Note that they have grown to this height since they were planted in 2001-2002.
Tree height = __________ feet.
Interpretive sign #5.
Stream meanders exist all along the stream within this park, but were not present before the 2001-2002
restoration project. Replacing the artificially straight stream with the meandering pattern added about
300’ of length to the stream, also creating a flatter slope to the channel.
13. What is the benefit of the stream meanders and the flatter slope?
________________________________________________________________________
________________________________________________________________________
Interpretive sign #6.
You have been walking all along the “forested riparian buffer.” The trees you see are Pennsylvania
native species that were planted in 2001-2002. Think about the various benefits of the streamside trees
and then:
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14. Name three benefits of a forested stream corridor:
_________________________________________________
_________________________________________________
_________________________________________________
Interpretive sign #7.
This wetland was restored by blocking an old drainage ditch, allowing water to stay within the wetland
for a few days before flowing into the stream. Water enters the wetland from a limestone spring, flows
through the wetland, and exits into Burd Run. The spring water is polluted with excess nutrients, but
water quality is substantially improved within the wetland, as nutrients are removed from the water.
15. What is the key nutrient that is removed in this wetland?
___________________________
16. Why is this nutrient a concern?
________________________________________________________________________
________________________________________________________________________
Conclusion
As you complete the trail toward the parking lot, look for the limestone spring that generates the flow
of water into the wetland (near some trees, across Fogelsonger Road from the wood-sided house).
17. Why do you think the groundwater flowing from the spring is polluted with excess nutrients?
Provide a brief explanation, noting the surrounding land use that contributes nutrients and key
characteristics of the bedrock geology based upon your observations about the limestone from the
trail beginning.
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
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Glossary
bedding planes – upper and lower surfaces of a sedimentary rock layer – the contact area between two layers of rock.
cut bank – the outside of a meander bend where high flow energy causes bank erosion and channel migration.
dip – the angle at which a geologic structure, such as a bedding plane, dips into the ground (relative to a horizontal plane).
forested riparian buffer – a streamside area planted to trees to provide a buffer between adjacent land uses (e.g. farming,
urban development) and the stream channel.
joint – a fracture within bedrock, often found in sets of many parallel fractures.
live stakes – trees planted by driving a cutting (essentially a stick about 3’ long and 1-2 inches in diameter) into the ground,
where it will sprout roots and new shoots. This planting technique is common along restored stream channels.
log vanes – logs placed into the stream bank and extending into the stream channel such that they will direct the flow away
from the bank and toward the center of the channel. Water cascading over these structures often creates a small plunge pool
on the downstream side, adding diversity to aquatic habitat.
meanders – bends in a stream channel. Meanders form naturally as part of the process that generates an equilibrium
between flow velocity, erosive energy, and sediment transport.
point bar – a deposit of sediment on the inside of a meander bend.
pools - deeper sections of the stream with slow-moving water
rip-rap – rocks placed along a stream bank (or lakeshore, oceanfront, etc.) to protect against bank erosion. Rip-rap is sized
such that expected flows will not erode or transport the rocks (i.e. they won’t move).
riffles - shallower sections of the stream with faster-moving water
rock vanes – similar to log vanes, but constructed from placed rocks.
root wads – the root end of a tree, including 10-15’ of the tree trunk, placed in the stream bank with the root end exposed in
the bank / stream water in order to provide protection against bank erosion. The roots also provide aquatic habitat for small
fish and other organisms.
spring – a location where water flows from the ground back onto the surface
vortex rock weir – a rock structure shaped like a chevron (
^ ) with the center in the middle of the stream channel and
pointing upstream. Water flowing over the structure is directed toward the center of the stream channel, protecting banks
from erosion and creating a small plunge pool below the structure.